The invention relates to a method for suctioning liquid fuel from a liquid trap in a fuel tank of a motor vehicle, in which liquid fuel is separated and collected in a collection chamber during ventilation of the fuel tank. The invention further relates to a fuel system for a motor vehicle, including a fuel tank, a liquid trap situated in the fuel tank for separating liquid fuel during ventilation of the fuel tank, wherein the liquid trap includes a collection chamber for the extracted fuel.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Fuel tanks of modern motor vehicles are usually designed as pressure tanks that are provided with a tank venting system, which on one hand prevents that an undesirable positive or negative pressure is established as a result of evaporation or condensation of fuel in the gas compartment or headspace due an increase or decrease of the ambient temperature, and on the other hand allows escape of the gas or gas mixture displaced by the fuel from the gas compartment or headspace of the fuel tank during refueling.
The tank venting system may include several tank vent valves distributed in the gas compartment or headspace, a liquid trap situated within the tank and connected by lines to the tank vent valves, a tank shutoff valve connected to the liquid trap, and an activated carbon filter situated outside of the tank between the tank shutoff valve and the environment. The tank shutoff valve is usually closed and is opened when refueling the fuel tank to carry the gas mixture that is displaced by the fuel from the gas compartment or headspace to the activated carbon filter which prevents an undesirable leakage of hydrocarbons into the environment.
Due to the fact that the gas or gas mixture displaced by the fuel during venting of the fuel tank does not only contain volatile but also liquid components of hydrocarbons in the form of small droplets that may damage the activated carbon filter, they have to be separated before the gas mixture escapes from the fuel tank. This function is fulfilled by the liquid trap, which is designed as a liquid separator or siphon. The liquid trap is usually situated within the fuel tank and communicates with the tank vent valves and the tank shutoff valve. In order to ensure a proper refueling of the fuel tank, the liquid fuel separated in the liquid trap has to be suctioned off, which in many tank venting devices is accomplished by an ejector pump, as for instance disclosed in EP 1 518 739 A2.
However, ejector pumps have several drawbacks. For example ejector pumps are pressure-sensitive and may not properly function in the case of a pressure decrease or pressure regulation in the fuel tank. They are also permanently consuming energy without significantly emptying the collection container and also require a complex construction to avoid leakages and an entering of fuel into the at least temporarily submerged liquid traps.
It would therefore be desirable and advantageous to provide an improved fuel system so that emptying of the liquid trap is possible also without the need for ejector pumps and in a simple manner.